4.9.3 Metabolic and Endocrine Disease Models

Metabolic disease models are central to antidiabetic, anti-obesity, and lipid-lowering drug development, and increasingly incorporate dietary as well as...

Metabolic disease models are central to antidiabetic, anti-obesity, and lipid-lowering drug development, and increasingly incorporate dietary as well as chemical induction methods to better reflect the multifactorial aetiology of human metabolic disease.

Diabetes Mellitus — Streptozotocin (STZ)-Induced Model

Diabetes mellitus is characterised by chronic hyperglycaemia resulting from insufficient insulin secretion, insulin resistance, or both. The streptozotocin-induced model exploits the selective uptake of STZ by pancreatic beta cells via the GLUT2 glucose transporter, followed by DNA alkylation and beta-cell necrosis; a single intraperitoneal dose (commonly 45–60 mg/kg, freshly prepared in citrate buffer at pH 4.5 and administered within minutes of preparation owing to the compound's instability in solution) produces a Type 1-like insulin-deficient diabetic state in rats within 48–72 hours, confirmed by fasting blood glucose exceeding 250 mg/dL. A combined high-fat-diet-plus-low-dose-STZ protocol instead produces a Type 2-like model incorporating both insulin resistance and partial beta-cell dysfunction, more closely reflecting the pathophysiology of the more common human disease form. Disease progression and drug efficacy are monitored via fasting blood glucose, the oral glucose tolerance test (OGTT), glycated haemoglobin (HbA1c), and serum insulin, with metformin, glibenclamide, or insulin serving as standard reference comparators depending on the mechanism under study. This model's principal advantage is its rapid onset and low cost; its principal limitation is that classical high-dose STZ diabetes does not reproduce the autoimmune beta-cell destruction underlying human Type 1 diabetes, for which the non-obese diabetic (NOD) mouse is a more mechanistically faithful, if considerably slower and more expensive, alternative.

Obesity — High-Fat Diet-Induced Model

Diet-induced obesity is modelled by feeding rodents, most commonly C57BL/6 mice owing to their well-documented diet-responsiveness, a palatable high-fat diet (typically providing 45–60% of calories from fat) ad libitum for eight to sixteen weeks, producing progressive weight gain, adiposity, and the metabolic sequelae of human dietary obesity, including insulin resistance, dyslipidaemia, and hepatic steatosis. Efficacy of candidate anti-obesity agents is assessed through body weight trajectory, body composition (by dual-energy X-ray absorptiometry or nuclear magnetic resonance), food intake, and the metabolic parameters described above. Orlistat and, increasingly, GLP-1 receptor agonists such as liraglutide serve as clinically relevant reference comparators. The principal strength of this model is its aetiological similarity to the dietary and lifestyle origins of most human obesity; its main limitation is the considerable inter-individual variability in weight gain typically observed even among genetically identical animals fed an identical diet, necessitating larger group sizes than many other metabolic models to achieve adequate statistical power.

Hyperlipidaemia — Triton WR-1339 and High-Fat Diet Models

Hyperlipidaemia, an elevation of circulating cholesterol and/or triglycerides, is modelled acutely using Triton WR-1339 (a non-ionic detergent administered intravenously or intraperitoneally at approximately 100–400 mg/kg), which transiently blocks lipoprotein lipase activity and produces a rapid, reproducible rise in serum triglycerides and cholesterol within 24 hours, suitable for rapid screening of hypolipidaemic candidates. Chronic hyperlipidaemia is alternatively modelled through prolonged high-fat, high-cholesterol dietary feeding, which more closely reproduces the gradual dyslipidaemia of human diet-related hyperlipidaemia and is often combined with atherosclerosis endpoint assessment (aortic lipid staining) in more advanced study designs. Serum total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides are the standard biochemical endpoints, with statins (for example atorvastatin) or fibrates serving as reference hypolipidaemic comparators. The Triton model offers speed and reproducibility for initial screening, while the dietary model offers superior translational relevance for candidates intended for chronic human use.

Osteoporosis — Ovariectomised (OVX) Rat Model

Postmenopausal osteoporosis results from the loss of the bone-protective effects of oestrogen following the menopausal decline in ovarian hormone production. The ovariectomised rat model surgically removes both ovaries, producing an oestrogen-deficient state that closely parallels human menopause and results in progressive trabecular bone loss over eight to twelve weeks, most prominently in the proximal tibia and lumbar vertebrae. Bone status is assessed using dual-energy X-ray absorptiometry (bone mineral density), micro-computed tomography (trabecular microarchitecture), biomechanical testing (femoral neck or vertebral compression strength), and biochemical markers of bone turnover (serum osteocalcin as a formation marker, and urinary deoxypyridinoline or serum C-telopeptide as resorption markers). Standard reference comparators include oestrogen replacement therapy, bisphosphonates (alendronate), and selective oestrogen receptor modulators (raloxifene). This model is considered the gold-standard preclinical model for postmenopausal osteoporosis research and is explicitly recommended by regulatory guidance for osteoporosis drug development, though the extended study duration required to observe measurable bone loss represents a practical limitation.